Customer on eBay can’t use but it now feature – gets error message

I am selling a modem on eBay, no one has bid on it yet and I listed it under “buy it now” for $70. A customer wants to use the buy it now option but has messaged me saying that try receive an error message stating that I cannot receive payments at this time. I’ve sold on eBay many times and have had customers purchase from me using the buy it now feature without any problems. I just received a payment (not for an eBay item) this week via paypal so it should work, yet I called eBay and they said there was no problem. Why is my cutomer getting this error message and how do I fix it?